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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2009 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.util.concurrent;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import com.google.common.annotations.Beta;<a name="line.19"></a>
<span class="sourceLineNo">020</span><a name="line.20"></a>
<span class="sourceLineNo">021</span>import java.util.concurrent.ExecutionException;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import java.util.concurrent.Executor;<a name="line.22"></a>
<span class="sourceLineNo">023</span><a name="line.23"></a>
<span class="sourceLineNo">024</span>/**<a name="line.24"></a>
<span class="sourceLineNo">025</span> * An object with an operational state, plus asynchronous {@link #start()} and {@link #stop()}<a name="line.25"></a>
<span class="sourceLineNo">026</span> * lifecycle methods to transition between states. Example services include webservers, RPC servers<a name="line.26"></a>
<span class="sourceLineNo">027</span> * and timers.<a name="line.27"></a>
<span class="sourceLineNo">028</span> *<a name="line.28"></a>
<span class="sourceLineNo">029</span> * &lt;p&gt;The normal lifecycle of a service is:<a name="line.29"></a>
<span class="sourceLineNo">030</span> * &lt;ul&gt;<a name="line.30"></a>
<span class="sourceLineNo">031</span> *   &lt;li&gt;{@linkplain State#NEW NEW} -&amp;gt;<a name="line.31"></a>
<span class="sourceLineNo">032</span> *   &lt;li&gt;{@linkplain State#STARTING STARTING} -&amp;gt;<a name="line.32"></a>
<span class="sourceLineNo">033</span> *   &lt;li&gt;{@linkplain State#RUNNING RUNNING} -&amp;gt;<a name="line.33"></a>
<span class="sourceLineNo">034</span> *   &lt;li&gt;{@linkplain State#STOPPING STOPPING} -&amp;gt;<a name="line.34"></a>
<span class="sourceLineNo">035</span> *   &lt;li&gt;{@linkplain State#TERMINATED TERMINATED}<a name="line.35"></a>
<span class="sourceLineNo">036</span> * &lt;/ul&gt;<a name="line.36"></a>
<span class="sourceLineNo">037</span> *<a name="line.37"></a>
<span class="sourceLineNo">038</span> * &lt;p&gt;There are deviations from this if there are failures or if {@link Service#stop} is called<a name="line.38"></a>
<span class="sourceLineNo">039</span> * before the {@link Service} reaches the {@linkplain State#RUNNING RUNNING} state. The set of legal<a name="line.39"></a>
<span class="sourceLineNo">040</span> * transitions form a &lt;a href="http://en.wikipedia.org/wiki/Directed_acyclic_graph"&gt;DAG&lt;/a&gt;,<a name="line.40"></a>
<span class="sourceLineNo">041</span> * therefore every method of the listener will be called at most once. N.B. The {@link State#FAILED}<a name="line.41"></a>
<span class="sourceLineNo">042</span> * and {@link State#TERMINATED} states are terminal states, once a service enters either of these<a name="line.42"></a>
<span class="sourceLineNo">043</span> * states it cannot ever leave them.<a name="line.43"></a>
<span class="sourceLineNo">044</span> *<a name="line.44"></a>
<span class="sourceLineNo">045</span> * &lt;p&gt;Implementors of this interface are strongly encouraged to extend one of the abstract classes<a name="line.45"></a>
<span class="sourceLineNo">046</span> * in this package which implement this interface and make the threading and state management<a name="line.46"></a>
<span class="sourceLineNo">047</span> * easier.<a name="line.47"></a>
<span class="sourceLineNo">048</span> *<a name="line.48"></a>
<span class="sourceLineNo">049</span> * @author Jesse Wilson<a name="line.49"></a>
<span class="sourceLineNo">050</span> * @author Luke Sandberg<a name="line.50"></a>
<span class="sourceLineNo">051</span> * @since 9.0 (in 1.0 as {@code com.google.common.base.Service})<a name="line.51"></a>
<span class="sourceLineNo">052</span> */<a name="line.52"></a>
<span class="sourceLineNo">053</span>@Beta<a name="line.53"></a>
<span class="sourceLineNo">054</span>public interface Service {<a name="line.54"></a>
<span class="sourceLineNo">055</span>  /**<a name="line.55"></a>
<span class="sourceLineNo">056</span>   * If the service state is {@link State#NEW}, this initiates service startup and returns<a name="line.56"></a>
<span class="sourceLineNo">057</span>   * immediately. If the service has already been started, this method returns immediately without<a name="line.57"></a>
<span class="sourceLineNo">058</span>   * taking action. A stopped service may not be restarted.<a name="line.58"></a>
<span class="sourceLineNo">059</span>   *<a name="line.59"></a>
<span class="sourceLineNo">060</span>   * @return a future for the startup result, regardless of whether this call initiated startup.<a name="line.60"></a>
<span class="sourceLineNo">061</span>   *         Calling {@link ListenableFuture#get} will block until the service has finished<a name="line.61"></a>
<span class="sourceLineNo">062</span>   *         starting, and returns one of {@link State#RUNNING}, {@link State#STOPPING} or<a name="line.62"></a>
<span class="sourceLineNo">063</span>   *         {@link State#TERMINATED}. If the service fails to start, {@link ListenableFuture#get}<a name="line.63"></a>
<span class="sourceLineNo">064</span>   *         will throw an {@link ExecutionException}, and the service's state will be<a name="line.64"></a>
<span class="sourceLineNo">065</span>   *         {@link State#FAILED}. If it has already finished starting, {@link ListenableFuture#get}<a name="line.65"></a>
<span class="sourceLineNo">066</span>   *         returns immediately. Cancelling this future has no effect on the service.<a name="line.66"></a>
<span class="sourceLineNo">067</span>   */<a name="line.67"></a>
<span class="sourceLineNo">068</span>  ListenableFuture&lt;State&gt; start();<a name="line.68"></a>
<span class="sourceLineNo">069</span><a name="line.69"></a>
<span class="sourceLineNo">070</span>  /**<a name="line.70"></a>
<span class="sourceLineNo">071</span>   * Initiates service startup (if necessary), returning once the service has finished starting.<a name="line.71"></a>
<span class="sourceLineNo">072</span>   * Unlike calling {@code start().get()}, this method throws no checked exceptions, and it cannot<a name="line.72"></a>
<span class="sourceLineNo">073</span>   * be {@linkplain Thread#interrupt interrupted}.<a name="line.73"></a>
<span class="sourceLineNo">074</span>   *<a name="line.74"></a>
<span class="sourceLineNo">075</span>   * @throws UncheckedExecutionException if startup failed<a name="line.75"></a>
<span class="sourceLineNo">076</span>   * @return the state of the service when startup finished.<a name="line.76"></a>
<span class="sourceLineNo">077</span>   */<a name="line.77"></a>
<span class="sourceLineNo">078</span>  State startAndWait();<a name="line.78"></a>
<span class="sourceLineNo">079</span><a name="line.79"></a>
<span class="sourceLineNo">080</span>  /**<a name="line.80"></a>
<span class="sourceLineNo">081</span>   * Returns {@code true} if this service is {@linkplain State#RUNNING running}.<a name="line.81"></a>
<span class="sourceLineNo">082</span>   */<a name="line.82"></a>
<span class="sourceLineNo">083</span>  boolean isRunning();<a name="line.83"></a>
<span class="sourceLineNo">084</span><a name="line.84"></a>
<span class="sourceLineNo">085</span>  /**<a name="line.85"></a>
<span class="sourceLineNo">086</span>   * Returns the lifecycle state of the service.<a name="line.86"></a>
<span class="sourceLineNo">087</span>   */<a name="line.87"></a>
<span class="sourceLineNo">088</span>  State state();<a name="line.88"></a>
<span class="sourceLineNo">089</span><a name="line.89"></a>
<span class="sourceLineNo">090</span>  /**<a name="line.90"></a>
<span class="sourceLineNo">091</span>   * If the service is {@linkplain State#STARTING starting} or {@linkplain State#RUNNING running},<a name="line.91"></a>
<span class="sourceLineNo">092</span>   * this initiates service shutdown and returns immediately. If the service is<a name="line.92"></a>
<span class="sourceLineNo">093</span>   * {@linkplain State#NEW new}, it is {@linkplain State#TERMINATED terminated} without having been<a name="line.93"></a>
<span class="sourceLineNo">094</span>   * started nor stopped. If the service has already been stopped, this method returns immediately<a name="line.94"></a>
<span class="sourceLineNo">095</span>   * without taking action.<a name="line.95"></a>
<span class="sourceLineNo">096</span>   *<a name="line.96"></a>
<span class="sourceLineNo">097</span>   * @return a future for the shutdown result, regardless of whether this call initiated shutdown.<a name="line.97"></a>
<span class="sourceLineNo">098</span>   *         Calling {@link ListenableFuture#get} will block until the service has finished shutting<a name="line.98"></a>
<span class="sourceLineNo">099</span>   *         down, and either returns {@link State#TERMINATED} or throws an<a name="line.99"></a>
<span class="sourceLineNo">100</span>   *         {@link ExecutionException}. If it has already finished stopping,<a name="line.100"></a>
<span class="sourceLineNo">101</span>   *         {@link ListenableFuture#get} returns immediately. Cancelling this future has no effect<a name="line.101"></a>
<span class="sourceLineNo">102</span>   *         on the service.<a name="line.102"></a>
<span class="sourceLineNo">103</span>   */<a name="line.103"></a>
<span class="sourceLineNo">104</span>  ListenableFuture&lt;State&gt; stop();<a name="line.104"></a>
<span class="sourceLineNo">105</span><a name="line.105"></a>
<span class="sourceLineNo">106</span>  /**<a name="line.106"></a>
<span class="sourceLineNo">107</span>   * Initiates service shutdown (if necessary), returning once the service has finished stopping. If<a name="line.107"></a>
<span class="sourceLineNo">108</span>   * this is {@link State#STARTING}, startup will be cancelled. If this is {@link State#NEW}, it is<a name="line.108"></a>
<span class="sourceLineNo">109</span>   * {@link State#TERMINATED terminated} without having been started nor stopped. Unlike calling<a name="line.109"></a>
<span class="sourceLineNo">110</span>   * {@code stop().get()}, this method throws no checked exceptions.<a name="line.110"></a>
<span class="sourceLineNo">111</span>   *<a name="line.111"></a>
<span class="sourceLineNo">112</span>   * @throws UncheckedExecutionException if the service has failed or fails during shutdown<a name="line.112"></a>
<span class="sourceLineNo">113</span>   * @return the state of the service when shutdown finished.<a name="line.113"></a>
<span class="sourceLineNo">114</span>   */<a name="line.114"></a>
<span class="sourceLineNo">115</span>  State stopAndWait();<a name="line.115"></a>
<span class="sourceLineNo">116</span><a name="line.116"></a>
<span class="sourceLineNo">117</span>  /**<a name="line.117"></a>
<span class="sourceLineNo">118</span>   * Registers a {@link Listener} to be {@linkplain Executor#execute executed} on the given<a name="line.118"></a>
<span class="sourceLineNo">119</span>   * executor.  The listener will have the corresponding transition method called whenever the<a name="line.119"></a>
<span class="sourceLineNo">120</span>   * service changes state. The listener will not have previous state changes replayed, so it is<a name="line.120"></a>
<span class="sourceLineNo">121</span>   * suggested that listeners are added before the service starts.<a name="line.121"></a>
<span class="sourceLineNo">122</span>   *<a name="line.122"></a>
<span class="sourceLineNo">123</span>   * &lt;p&gt;There is no guaranteed ordering of execution of listeners, but any listener added through<a name="line.123"></a>
<span class="sourceLineNo">124</span>   * this method is guaranteed to be called whenever there is a state change.<a name="line.124"></a>
<span class="sourceLineNo">125</span>   *<a name="line.125"></a>
<span class="sourceLineNo">126</span>   * &lt;p&gt;Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown<a name="line.126"></a>
<span class="sourceLineNo">127</span>   * during {@code Executor.execute} (e.g., a {@code RejectedExecutionException} or an exception<a name="line.127"></a>
<span class="sourceLineNo">128</span>   * thrown by {@linkplain MoreExecutors#sameThreadExecutor inline execution}) will be caught and<a name="line.128"></a>
<span class="sourceLineNo">129</span>   * logged.<a name="line.129"></a>
<span class="sourceLineNo">130</span>   *<a name="line.130"></a>
<span class="sourceLineNo">131</span>   * @param listener the listener to run when the service changes state is complete<a name="line.131"></a>
<span class="sourceLineNo">132</span>   * @param executor the executor in which the the listeners callback methods will be run. For fast,<a name="line.132"></a>
<span class="sourceLineNo">133</span>   *     lightweight listeners that would be safe to execute in any thread, consider<a name="line.133"></a>
<span class="sourceLineNo">134</span>   *     {@link MoreExecutors#sameThreadExecutor}.<a name="line.134"></a>
<span class="sourceLineNo">135</span>   * @since 13.0<a name="line.135"></a>
<span class="sourceLineNo">136</span>   */<a name="line.136"></a>
<span class="sourceLineNo">137</span>  void addListener(Listener listener, Executor executor);<a name="line.137"></a>
<span class="sourceLineNo">138</span><a name="line.138"></a>
<span class="sourceLineNo">139</span>  /**<a name="line.139"></a>
<span class="sourceLineNo">140</span>   * The lifecycle states of a service.<a name="line.140"></a>
<span class="sourceLineNo">141</span>   *<a name="line.141"></a>
<span class="sourceLineNo">142</span>   * @since 9.0 (in 1.0 as {@code com.google.common.base.Service.State})<a name="line.142"></a>
<span class="sourceLineNo">143</span>   */<a name="line.143"></a>
<span class="sourceLineNo">144</span>  @Beta // should come out of Beta when Service does<a name="line.144"></a>
<span class="sourceLineNo">145</span>  enum State {<a name="line.145"></a>
<span class="sourceLineNo">146</span>    /**<a name="line.146"></a>
<span class="sourceLineNo">147</span>     * A service in this state is inactive. It does minimal work and consumes<a name="line.147"></a>
<span class="sourceLineNo">148</span>     * minimal resources.<a name="line.148"></a>
<span class="sourceLineNo">149</span>     */<a name="line.149"></a>
<span class="sourceLineNo">150</span>    NEW,<a name="line.150"></a>
<span class="sourceLineNo">151</span><a name="line.151"></a>
<span class="sourceLineNo">152</span>    /**<a name="line.152"></a>
<span class="sourceLineNo">153</span>     * A service in this state is transitioning to {@link #RUNNING}.<a name="line.153"></a>
<span class="sourceLineNo">154</span>     */<a name="line.154"></a>
<span class="sourceLineNo">155</span>    STARTING,<a name="line.155"></a>
<span class="sourceLineNo">156</span><a name="line.156"></a>
<span class="sourceLineNo">157</span>    /**<a name="line.157"></a>
<span class="sourceLineNo">158</span>     * A service in this state is operational.<a name="line.158"></a>
<span class="sourceLineNo">159</span>     */<a name="line.159"></a>
<span class="sourceLineNo">160</span>    RUNNING,<a name="line.160"></a>
<span class="sourceLineNo">161</span><a name="line.161"></a>
<span class="sourceLineNo">162</span>    /**<a name="line.162"></a>
<span class="sourceLineNo">163</span>     * A service in this state is transitioning to {@link #TERMINATED}.<a name="line.163"></a>
<span class="sourceLineNo">164</span>     */<a name="line.164"></a>
<span class="sourceLineNo">165</span>    STOPPING,<a name="line.165"></a>
<span class="sourceLineNo">166</span><a name="line.166"></a>
<span class="sourceLineNo">167</span>    /**<a name="line.167"></a>
<span class="sourceLineNo">168</span>     * A service in this state has completed execution normally. It does minimal work and consumes<a name="line.168"></a>
<span class="sourceLineNo">169</span>     * minimal resources.<a name="line.169"></a>
<span class="sourceLineNo">170</span>     */<a name="line.170"></a>
<span class="sourceLineNo">171</span>    TERMINATED,<a name="line.171"></a>
<span class="sourceLineNo">172</span><a name="line.172"></a>
<span class="sourceLineNo">173</span>    /**<a name="line.173"></a>
<span class="sourceLineNo">174</span>     * A service in this state has encountered a problem and may not be operational. It cannot be<a name="line.174"></a>
<span class="sourceLineNo">175</span>     * started nor stopped.<a name="line.175"></a>
<span class="sourceLineNo">176</span>     */<a name="line.176"></a>
<span class="sourceLineNo">177</span>    FAILED<a name="line.177"></a>
<span class="sourceLineNo">178</span>  }<a name="line.178"></a>
<span class="sourceLineNo">179</span><a name="line.179"></a>
<span class="sourceLineNo">180</span>  /**<a name="line.180"></a>
<span class="sourceLineNo">181</span>   * A listener for the various state changes that a {@link Service} goes through in its lifecycle.<a name="line.181"></a>
<span class="sourceLineNo">182</span>   *<a name="line.182"></a>
<span class="sourceLineNo">183</span>   * @author Luke Sandberg<a name="line.183"></a>
<span class="sourceLineNo">184</span>   * @since 13.0<a name="line.184"></a>
<span class="sourceLineNo">185</span>   */<a name="line.185"></a>
<span class="sourceLineNo">186</span>  @Beta // should come out of Beta when Service does<a name="line.186"></a>
<span class="sourceLineNo">187</span>  interface Listener {<a name="line.187"></a>
<span class="sourceLineNo">188</span>    /**<a name="line.188"></a>
<span class="sourceLineNo">189</span>     * Called when the service transitions from {@linkplain State#NEW NEW} to<a name="line.189"></a>
<span class="sourceLineNo">190</span>     * {@linkplain State#STARTING STARTING}. This occurs when {@link Service#start} or<a name="line.190"></a>
<span class="sourceLineNo">191</span>     * {@link Service#startAndWait} is called the first time.<a name="line.191"></a>
<span class="sourceLineNo">192</span>     */<a name="line.192"></a>
<span class="sourceLineNo">193</span>    void starting();<a name="line.193"></a>
<span class="sourceLineNo">194</span><a name="line.194"></a>
<span class="sourceLineNo">195</span>    /**<a name="line.195"></a>
<span class="sourceLineNo">196</span>     * Called when the service transitions from {@linkplain State#STARTING STARTING} to<a name="line.196"></a>
<span class="sourceLineNo">197</span>     * {@linkplain State#RUNNING RUNNING}. This occurs when a service has successfully started.<a name="line.197"></a>
<span class="sourceLineNo">198</span>     */<a name="line.198"></a>
<span class="sourceLineNo">199</span>    void running();<a name="line.199"></a>
<span class="sourceLineNo">200</span><a name="line.200"></a>
<span class="sourceLineNo">201</span>    /**<a name="line.201"></a>
<span class="sourceLineNo">202</span>     * Called when the service transitions to the {@linkplain State#STOPPING STOPPING} state. The<a name="line.202"></a>
<span class="sourceLineNo">203</span>     * only valid values for {@code from} are {@linkplain State#STARTING STARTING} or<a name="line.203"></a>
<span class="sourceLineNo">204</span>     * {@linkplain State#RUNNING RUNNING}.  This occurs when {@link Service#stop} is called.<a name="line.204"></a>
<span class="sourceLineNo">205</span>     *<a name="line.205"></a>
<span class="sourceLineNo">206</span>     * @param from The previous state that is being transitioned from.<a name="line.206"></a>
<span class="sourceLineNo">207</span>     */<a name="line.207"></a>
<span class="sourceLineNo">208</span>    void stopping(State from);<a name="line.208"></a>
<span class="sourceLineNo">209</span><a name="line.209"></a>
<span class="sourceLineNo">210</span>    /**<a name="line.210"></a>
<span class="sourceLineNo">211</span>     * Called when the service transitions to the {@linkplain State#TERMINATED TERMINATED} state.<a name="line.211"></a>
<span class="sourceLineNo">212</span>     * The {@linkplain State#TERMINATED TERMINATED} state is a terminal state in the transition<a name="line.212"></a>
<span class="sourceLineNo">213</span>     * diagram.  Therefore, if this method is called, no other methods will be called on the<a name="line.213"></a>
<span class="sourceLineNo">214</span>     * {@link Listener}.<a name="line.214"></a>
<span class="sourceLineNo">215</span>     *<a name="line.215"></a>
<span class="sourceLineNo">216</span>     * @param from The previous state that is being transitioned from.  The only valid values for<a name="line.216"></a>
<span class="sourceLineNo">217</span>     *     this are {@linkplain State#NEW NEW}, {@linkplain State#RUNNING RUNNING} or<a name="line.217"></a>
<span class="sourceLineNo">218</span>     *     {@linkplain State#STOPPING STOPPING}.<a name="line.218"></a>
<span class="sourceLineNo">219</span>     */<a name="line.219"></a>
<span class="sourceLineNo">220</span>    void terminated(State from);<a name="line.220"></a>
<span class="sourceLineNo">221</span><a name="line.221"></a>
<span class="sourceLineNo">222</span>    /**<a name="line.222"></a>
<span class="sourceLineNo">223</span>     * Called when the service transitions to the {@linkplain State#FAILED FAILED} state. The<a name="line.223"></a>
<span class="sourceLineNo">224</span>     * {@linkplain State#FAILED FAILED} state is a terminal state in the transition diagram.<a name="line.224"></a>
<span class="sourceLineNo">225</span>     * Therefore, if this method is called, no other methods will be called on the {@link Listener}.<a name="line.225"></a>
<span class="sourceLineNo">226</span>     *<a name="line.226"></a>
<span class="sourceLineNo">227</span>     * @param from The previous state that is being transitioned from.  Failure can occur in any<a name="line.227"></a>
<span class="sourceLineNo">228</span>     *     state with the exception of {@linkplain State#NEW NEW} or<a name="line.228"></a>
<span class="sourceLineNo">229</span>     *     {@linkplain State#TERMINATED TERMINATED}.<a name="line.229"></a>
<span class="sourceLineNo">230</span>     * @param failure The exception that caused the failure.<a name="line.230"></a>
<span class="sourceLineNo">231</span>     */<a name="line.231"></a>
<span class="sourceLineNo">232</span>    void failed(State from, Throwable failure);<a name="line.232"></a>
<span class="sourceLineNo">233</span>  }<a name="line.233"></a>
<span class="sourceLineNo">234</span>}<a name="line.234"></a>




























































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